1. Technical Field
The invention relates to an electret loudspeaker device. Particularly, the invention relates to a design that is capable of shaping a directionality of an emitted sound field of an electret loudspeaker device.
2. Related Art
An electret loudspeaker device uses an electrostatic field of an electret diaphragm to transform audio signals of different potentials coming from an electrode layer into a sound field. FIG. 1A is an exploded view of a conventional electret loudspeaker device. FIG. 1B is a side view of the electret loudspeaker device of FIG. 1A. Referring to FIG. 1A and FIG. 1B, in the conventional electret loudspeaker device 10, a first perforated electrode 12 is driven by an external signal to form a potential variation, so as to drive an electret diaphragm 11 to vibrate and produce a sound wave. In order to form a space between the electret diaphragm 11 and the first perforated electrode 12 so as to maintain a room for the electret diaphragm 11 to vibrate in the electret loudspeaker device, a first spacer 13 is disposed between the electret diaphragm 11 and the first perforated electrode 12. The first spacer 13 has a plurality of first openings 13a, and the first openings 13a carve out the space between the first perforated electrode 12 and the electret diaphragm 11 forming a plurality of chambers 10a, and when the electret diaphragm 11 is driven, it vibrates in the chamber 10a to produce a sound wave. Therefore, the electret loudspeaker device 10 is basically a loudspeaker device having a plurality of unit sounding cells arranged in an array with one chamber regarded as one unit.
Since the electret loudspeaker is inherently an array speaker device, as a result of interference from every sound wave coming from unit sounding cell, a sound field emitted from the electret loudspeaker device has inherently great directionality in the far field in nature. Although the loudspeaker with great directionality has some specific uses, the application of the electret loudspeaker device is limited as well. Therefore, design of directionality of the emitted sound field of the electret loudspeaker device is required, which allows the electret loudspeaker device could be designed to accommodate the application scenario and gets wider applications more than high directionality.